The present invention relates to the preparation of low-salt, low-TOC and perhaps low-gas water, in particular water of high quality.
In a large number of countries in the world there exists a shortage of potable water. This is particularly the case in dry regions and in regions where the infrastructure for careful preparation and transport of potable water is inadequate.
It is therefore generally important to manage potable water as economically as possible and to utilize possible potable water sources as well as possible.
The currently most used sources of potable water are groundwater, spring water and surface water which, after purification, can be used as potable water. In some cases rainwater is also used.
The object of the present invention is to provide means for the preparation of water from sources which until now have not been used. The attempt is hereby made to provide water of a high purity which can be used directly as boiler feed water or for other technical applications. The usual sources of potable water need hereby no longer be drawn upon for this use.
The attempt is further made to provide such a apparatus wherein efforts in respect of investment, energy consumption and other effort are minimal.
Known from EP-A-O 192 893 is a preparation apparatus for preparing water from water-containing gases released in a device for converting chemical energy into mechanical energy, wherein the preparation apparatus comprises:
at least one membrane which is adapted to at least partly allow passage of water molecules and substantially prevent passage of other molecules;
means for guiding the gases containing water vapour along a first side of the membrane,
discharge means arranged on the second side of the membrane for discharging the water released on the second side of the membrane.
This prior art publication relates to a conversion device with internal combustion. Such devices are used in large numbers in the form of combustion engines, both stationary and mobile. Heavy and bulky auxiliary equipment is required to prepare water from the exhaust gases of such a motor. A vacuum pump must thus be used to maintain a sufficiently low pressure on the second side of the membrane and a condenser must be used to allow a sufficiently low temperature to prevail on the second side of the membrane.
These are costly, heavy and bulky apparatuses which it is hardly possible to accommodate in a vehicle, certainly when provisions must be made for storage of the prepared water. This is already in no way proportional with the thus obtained yield of water. These drawbacks are also relevant in respect of stationary engines.
The object of the invention is to provide an application of such a preparation apparatus in a situation in which these drawbacks do not occur.
This object is achieved by such a preparation apparatus which is characterized in that the conversion device for converting chemical energy into mechanical energy is formed by a conversion device with external combustion, and in that the discharge means are formed at least partly by auxiliary equipment associated with the conversion device with external combustion.
These measures enable the use of the auxiliary equipment required in a conversion device for chemical energy to mechanical energy with external combustion. The external combustion supposes a Carnot cycle through which an auxiliary medium must progress as energy carrier. The progression through a Carnot cycle requires the presence of a condenser. A pump is usually present to cause an underpressure to prevail in the condenser.
The measures according to the invention enable the fruitful use of these facilities, so that these per se bulky appliances do not have to be placed separately.
It is thus possible to use a heretofore unused source of water of a high quality, i.e. gases containing water vapour, such as the waste gases of an energy conversion device. It is noted here that in the presently proposed use the prepared water is used as boiler feed water or as water for other industrial applications. This is the consequence of the high purity of the water attainable with the apparatus according to the invention. It is conceivable to use the water as potable water, i.e. after the addition of substances normally present in potable water, or by using membranes which allow through the substances in question.
According to a first embodiment the conversion device forms part of an electric power station.
A conversion device of exceptionally large dimensions is present here with a high rate of water-containing gas flows. The auxiliary equipment is moreover of corresponding dimensions, so that the additional load by the flow of the water preparation according to the invention has no or hardly any effect on the dimensioning of the auxiliary equipment. It is usually even possible to use this auxiliary equipment without modifications, so that it is easy to arrange such a water preparation apparatus in an existing power station.
In view of the exceptionally large quantities of flue gases which are produced by an electric power station, it is particularly attractive to use the flue gases as a source of water. As stated above, this results in large saving.
According to another embodiment the auxiliary equipment comprises a condenser and the discharge means re formed at least partly by the condenser associated with the auxiliary equipment.
According to a further embodiment the condenser is connected to a pump for maintaining a pressure in the condenser which is lower than the ambient pressure.
These measures also result in an effective use of components already present.
According to another preferred embodiment the membrane is only suitable for allowing through water molecules in vapour form. This has the consequence that on the discharge side of the membrane only water becomes available which has been in vapour phase, thus precluding the presence of substances dissolved or otherwise present in the water.
According to yet another preferred embodiment the membrane is formed into a number of substantially cylinder surface-shaped units, wherein the axes of each of the cylinder surfaces extend mutually parallel, and wherein at least one end of the cylinders is connected to a collecting tank forming part of the discharge means.
It will be apparent that in a large-scale application of the present invention, where the object is of course to achieve sufficient water output, the membrane will have to have as large a surface area as possible. It has been found that with the above stated measures a large surface area of the membrane can be realized within a relatively small volume, but wherein the dimensioning has yet to be determined. This in any case depends on the properties of the membrane, the thickness thereof, the flow rate of the gas from which the water must be extracted, pressures, temperatures and so on.
It is also possible in principle to apply other configurations of the membrane, such as a membrane in the form of a plate, a spiral and so on.
According to a preferred embodiment the substantially cylinder surface-shaped units are manufactured from hollow tubes or fibres of the membrane or from capillaries.
The initial processing of the membrane material into tubes or fibres makes it particularly possible to manufacture the above stated structure.
Another preferred embodiment teaches that the substantially cylinder surface-shaped units are placed with a vertical axis in a substantially vertically extending flue gas duct.
The advantages of the above stated configurations are hereby combined.
It is otherwise also possible to fold the axis of the cylinder surfaces horizontally.
When the apparatus is applied in a flue gas discharge duct of an incineration plant provided with a flue gas desulphurizing installation operating with water, the apparatus is preferably placed downstream of the flue gas desulphurizing installation.
Flue gas desulphurizing installations generally operate with large quantities of water, a part of which remains in the flue gases saturated with water vapour to be further released to the atmosphere. It is therefore important to place the apparatus according to the invention downstream of the flue gas desulphurizing installation in order to also enable recovery of the water fed into the flue gas desulphurizing installation.
It is also possible for the cooling means to be adapted to maintain a temperature below the dew point of water in the collecting tank.
Another measure teaches that the means for maintaining a low temperature on the second side of the membrane are adapted to make effective use of the heat released on the second side of the membrane. The efficiency of an electric power station can hereby be improved slightly.
A further improvement in efficiency is possible in that the water content of the flue gases is decreased. The danger of condensation occurring is also reduced. The need for additional heating of the flue gases before they are carried to the chimney in order to prevent condensation is hereby reduced.
An electric power plant not only produces water but also consumes considerable quantities of water as boiler feed water. The boiler feed water comes for the greater part from the condenser, so that a circulation is obtained. The circulation is however not completely closed, since water loss does occur. This water loss can be easily compensated with a apparatus according to the invention. A considerable saving of potable water is obtained herewith, since the boiler make-up water must be of high quality and pre-treated potable water or spring water, groundwater or surface water is normally used.